// Copyright (c) 2018, ETH Zurich and UNC Chapel Hill.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
//     * Neither the name of ETH Zurich and UNC Chapel Hill nor the names of
//       its contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Author: Johannes L. Schoenberger (jsch-at-demuc-dot-de)

#ifndef COLMAP_SRC_BASE_SCENE_CLUSTERING_H_
#define COLMAP_SRC_BASE_SCENE_CLUSTERING_H_

#include <list>
#include <vector>

#include "util/types.h"

namespace colmap {

// Scene clustering approach using normalized cuts on the scene graph. The scene
// is hierarchically partitioned into overlapping clusters until a maximum
// number of images is in a leaf node.
class SceneClustering 
{
public:
    struct Options 
    {
        // The branching factor of the hierarchical clustering.
        int branching = 2;

        // The number of overlapping images between child clusters.
        int image_overlap = 50;

        // The maximum number of images in a leaf node cluster, otherwise the
        // cluster is further partitioned using the given branching factor. Note
        // that a cluster leaf node will have at most `leaf_max_num_images +
        // overlap` images to satisfy the overlap constraint.
        int leaf_max_num_images = 500;

        bool Check() const;
    };

    struct Cluster 
    {
        std::vector<image_t> image_ids;
        std::vector<Cluster> child_clusters;
    };

    SceneClustering(const Options& options);

    void Partition(const std::vector<std::pair<image_t, image_t>>& image_pairs,
                   const std::vector<int>& num_inliers);

    const Cluster* GetRootCluster() const;
    std::vector<const Cluster*> GetLeafClusters() const;

private:
    void PartitionCluster(const std::vector<std::pair<int, int>>& edges,
                          const std::vector<int>& weights, Cluster* cluster);

    const Options options_;
    std::unique_ptr<Cluster> root_cluster_;
};

}  // namespace colmap

#endif  // COLMAP_SRC_BASE_SCENE_CLUSTERING_H_
